Respiration

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What is Respiration?

Cellular respiration is an exothermic reaction that occurs continuously in all living cells.
It releases the energy needed for living processes; this energy is transferred from glucose.
Respiration is a chemical process and is not the same as breathing.
Energy from respiration is used for: chemical reactions to build larger molecules, muscle contraction for movement, and keeping warm to maintain a constant temperature for enzyme activity.

Aerobic Respiration

Aerobic respiration uses oxygen to break down glucose completely, releasing a relatively large amount of energy.
Word equation: glucose + oxygen → carbon dioxide + water.
Balanced symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
Most aerobic respiration takes place in the mitochondria of cells.
The products carbon dioxide and water are waste products.

Balanced equation for aerobic respiration

Anaerobic Respiration in Animals

Anaerobic respiration takes place without oxygen and involves the incomplete breakdown of glucose.
In animals, glucose is broken down into lactic acid: glucose → lactic acid.
It releases much less energy than aerobic respiration because glucose is not fully oxidised.
It mainly occurs in muscle cells during vigorous exercise when oxygen supply cannot meet demand.
Lactic acid builds up, lowering the pH of muscle tissue and causing fatigue, so muscles stop contracting efficiently.

Anaerobic respiration in muscles during vigorous exercise: glucose -> lactic acid.

Anaerobic Respiration in Plants and Yeast

In plants and yeast, glucose is broken down without oxygen to produce ethanol and carbon dioxide: glucose → ethanol + carbon dioxide.
In yeast, this process is called fermentation.
Fermentation is economically important in bread making (carbon dioxide makes dough rise) and in brewing (ethanol is the alcohol in drinks).

Anaerobic respiration in yeast: glucose -> alcohol + carbon dioxide.

Comparing Aerobic and Anaerobic Respiration

Oxygen: aerobic requires oxygen; anaerobic does not.
Products: aerobic produces carbon dioxide and water; anaerobic in animals produces lactic acid; anaerobic in plants and yeast produces ethanol and carbon dioxide.
Energy transferred: aerobic releases much more energy than anaerobic.
Location: aerobic mainly in mitochondria; anaerobic in the cytoplasm.

Response to Exercise

During exercise, muscles contract more, increasing energy demand and the need for oxygen.
The body responds by increasing breathing rate and breath volume to absorb more oxygen and remove more carbon dioxide.
Heart rate also increases to supply more oxygenated blood to the muscles.
If oxygen supply is insufficient, anaerobic respiration occurs, producing lactic acid and creating an oxygen debt.
After vigorous exercise, breathing and heart rate remain elevated to deliver extra oxygen to break down lactic acid.

Oxygen Debt

Oxygen debt is the extra oxygen needed after exercise to react with accumulated lactic acid and remove it from cells.
Lactic acid can be oxidised to carbon dioxide and water, or transported in the blood to the liver where it is converted back into glucose.
Repaying the oxygen debt explains why breathing and heart rate stay high after exercise.

Metabolism

Metabolism is the sum of all reactions in a cell or the body.
Energy from respiration drives enzyme-controlled metabolic reactions that synthesise new molecules.
Carbohydrates: glucose is used to make starch (energy storage in plants), glycogen (energy storage in animals), and cellulose (strengthens plant cell walls).
Lipids: synthesised from glycerol and three fatty acids; used for energy storage.
Proteins: glucose and nitrate ions form amino acids, which are used to synthesise proteins; excess proteins are broken down to urea for excretion.

Practical: Investigating Respiration

Respirometers measure the rate of oxygen consumption during aerobic respiration in organisms such as germinating seeds or invertebrates.
Soda-lime pellets absorb carbon dioxide produced, so the volume change measured is due to oxygen consumption.
The apparatus is placed in a temperature-controlled water bath to investigate the effect of temperature.
The rate of oxygen consumption (cm³ min⁻¹) is calculated using the formula πr²h, where r is the radius of the capillary tube and h is the distance moved by the manometer fluid per minute.
The respirometer cannot measure anaerobic respiration because no oxygen is consumed.

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1.Which of the following would allow the net diffusion of oxygen into Amoeba proteus?
Easy
- Aconcentration of oxygen in water = 4 ppm, concentration of oxygen in Amoeba = 4 ppm
- Bconcentration of oxygen in water = 10 ppm, concentration of oxygen in Amoeba = 10 ppm
- Cconcentration of oxygen in water = 4 ppm, concentration of oxygen in Amoeba = 10 ppm
- Dconcentration of oxygen in water = 10 ppm, concentration of oxygen in Amoeba = 4 ppm
2.Which two changes allow the rate of respiration in the muscle to increase during exercise?
Medium
- Aheart rate increases and amount of glucose delivered to the muscles increases
- Bheart rate increases and amount of glucose delivered to the muscles decreases
- Cheart rate decreases and amount of glucose delivered to the muscles increases
- Dheart rate decreases and amount of glucose delivered to the muscles decreases
3.Respiration is a life process carried out by all organisms to release energy for cellular processes. State two uses, in an animal cell, of the energy released during respiration.
Easy
- AMuscle contraction and keeping warm
- BPhotosynthesis and transpiration
- CDigestion and excretion
- DBreathing and heart beating
4.Anaerobic respiration releases more energy per glucose molecule than aerobic respiration.
Easy
True or false?
5.Which word equation represents anaerobic respiration in yeast?
Easy
- Aglucose → lactic acid
- Bglucose → ethanol + carbon dioxide
- Cglucose + oxygen → carbon dioxide + water
- Dglucose → carbon dioxide + water
6.Which of the following statements about anaerobic respiration in animals are correct? (select all that apply)
Medium
- AIt produces lactic acid.
- BIt occurs when oxygen is absent.
- CIt releases more energy than aerobic respiration.
- DIt occurs in muscle cells during vigorous exercise.
- EIt produces ethanol and carbon dioxide.
7.Match each term with its correct description.
Easy
- Aerobic respiration
- Anaerobic respiration
- Oxygen debt
- Fermentation
- The amount of extra oxygen needed after exercise to break down lactic acid
- Respiration that uses oxygen
- Anaerobic respiration in yeast cells
- Respiration that occurs without oxygen
8.Place the following statements in the correct order to describe how oxygen debt is repaid after vigorous exercise.
Medium
- Lactic acid is transported in the blood from the muscles to the liver.
- Breathing rate and heart rate remain elevated to supply extra oxygen.
- Lactic acid is broken down using oxygen to produce carbon dioxide and water.
- The oxygen debt is repaid.

Thêm câu hỏi

9.Respiration is an exothermic reaction.
Easy
True or false?
10.Which of the following is the correct balanced chemical equation for aerobic respiration?
Medium
- AC6H12O6 + 6O2 → 6CO2 + 6H2O
- BC6H12O6 + O2 → CO2 + H2O
- C6C6H12O6 + 6O2 → 6CO2 + 6H2O
- DC6H12O6 + 6O2 → CO2 + H2O
11.Which of the following are reasons that organisms need the energy released by respiration? (select all that apply)
Medium
- AMuscle contraction to allow movement
- BChemical reactions to build larger molecules from smaller molecules
- CKeeping warm to maintain a constant temperature suitable for enzyme activity
- DProducing oxygen for the atmosphere
12.Which equation represents anaerobic respiration in yeast?
Easy
- Aglucose → ethanol + carbon dioxide
- Bglucose → lactic acid
- Cglucose + oxygen → carbon dioxide + water
- Dglucose → carbon dioxide + water
13.Which word describes a reaction that releases energy, such as respiration?
Easy
- AExothermic
- BEndothermic
- CExergonic
- DCatabolic
14.Cellular respiration is the same process as breathing.
Easy
True or false?
15.Which statement correctly compares aerobic and anaerobic respiration?
Medium
- AAerobic respiration releases more energy per glucose molecule than anaerobic respiration.
- BAnaerobic respiration releases more energy per glucose molecule than aerobic respiration.
- CBoth release the same amount of energy per glucose molecule.
- DAerobic respiration produces lactic acid, while anaerobic respiration produces ethanol.
16.Match each process with its correct word equation.
Medium
- Aerobic respiration
- Anaerobic respiration in animals
- Anaerobic respiration in yeast
- glucose + oxygen → carbon dioxide + water
- glucose → lactic acid
- glucose → ethanol + carbon dioxide
17.Place the following steps in the correct order to describe how oxygen debt is repaid after vigorous exercise.
Medium
- Lactic acid is transported in the blood from the muscles to the liver.
- Breathing rate and depth remain high to supply extra oxygen.
- Lactic acid is oxidised in the liver to carbon dioxide and water.
- The oxygen debt is repaid.
18.A respirometer is used to investigate the rate of respiration in germinating seeds. Which of the following statements about this practical are correct? (select all that apply)
Hard
- ASoda-lime pellets are used to absorb carbon dioxide produced.
- BThe rate of oxygen consumption is taken as the rate of respiration.
- CThe apparatus can be used to measure the rate of anaerobic respiration.
- DThe water bath is used to control temperature.
- EThe volume of oxygen consumed can be calculated using πr²h.
19.Match each metabolic process with its correct description.
Medium
- Synthesis of glycogen
- Synthesis of lipids
- Breakdown of excess proteins
- Synthesis of proteins
- Glucose is converted into a storage molecule in animals.
- Glycerol combines with three fatty acids.
- Urea is produced for excretion.
- Amino acids are joined together.
20.Which of the following is the correct balanced chemical equation for anaerobic respiration in yeast?
Medium
- AC₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
- BC₆H₁₂O₆ → 2C₂H₅OH + CO₂
- CC₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
- DC₆H₁₂O₆ → 2C₃H₆O₃
21.Anaerobic respiration in yeast is called fermentation.
Easy
True or false?
22.Which of the following are products of aerobic respiration? (select all that apply)
Medium
- ACarbon dioxide
- BWater
- CLactic acid
- DEthanol
- EOxygen
23.A respirometer contains germinating peas in a water bath at 25°C. In 10 minutes, the manometer fluid moves 4.0 cm along the capillary tube, which has a radius of 0.1 cm. Using πr²h, calculate the rate of oxygen consumption in cm³ min⁻¹. Use π = 3.14.
Medium
- A0.1256 cm³ min⁻¹
- B0.01256 cm³ min⁻¹
- C1.256 cm³ min⁻¹
- D0.314 cm³ min⁻¹
24.A respirometer is set up with germinating seeds and soda-lime pellets. The soda-lime absorbs the carbon dioxide produced. As the seeds respire aerobically, what happens to the manometer fluid and why?
Hard
- AIt moves towards the seeds because oxygen is taken in and carbon dioxide is absorbed
- BIt moves away from the seeds because carbon dioxide is produced and pushes the fluid
- CIt does not move because oxygen and carbon dioxide are produced in equal amounts
- DIt moves towards the seeds because carbon dioxide is taken in and oxygen is absorbed
25.In a respirometer investigation into the effect of temperature on the rate of respiration in germinating seeds, which of the following statements are correct? (select all that apply)
Hard
- AThe rate of respiration increases as temperature rises until the optimum temperature is reached
- BAt very high temperatures the enzymes controlling respiration become denatured and the rate falls
- CSoda-lime pellets are included to absorb the carbon dioxide produced
- DThe respirometer can also be used to measure the rate of anaerobic respiration
- EAt low temperatures the rate is low because enzyme and substrate molecules collide less frequently
26.Using the table, describe the trend in lactic acid concentration as running speed increases from 10 to 25 km h⁻¹.
Medium
- AIt stays constant until 18 km h⁻¹, then increases steeply
- BIt increases steadily from 10 km h⁻¹ to 25 km h⁻¹
- CIt decreases as running speed increases
- DIt increases until 18 km h⁻¹, then decreases
27.After vigorous exercise, a person continues to breathe deeply and rapidly for several minutes. Which statement best explains why?
Medium
- AExtra oxygen is needed to break down the accumulated lactic acid
- BExtra carbon dioxide is needed to break down the accumulated lactic acid
- CExtra oxygen is needed to convert glucose into lactic acid
- DExtra oxygen is needed to convert lactic acid into ethanol
28.During exercise, the heart rate and breathing rate increase to supply the muscles with more oxygenated blood.
Easy
True or false?
29.A student's heart rate during exercise is 160 beats per minute and their stroke volume is 0.16 dm³. Calculate the cardiac output using: cardiac output = stroke volume × heart rate.
Medium
- A25.6 dm³ min⁻¹
- B2.56 dm³ min⁻¹
- C256 dm³ min⁻¹
- D0.256 dm³ min⁻¹
30.Which of the following are ways in which the human body responds to the increased demand for energy during vigorous exercise? (select all that apply)
Medium
- AHeart rate increases
- BBreathing rate increases
- CBreath volume increases
- DThe body stops respiring anaerobically
- EMore oxygenated blood is delivered to the muscles
31.Match each metabolic process with the molecules it produces.
Medium
- Synthesis of glycogen
- Synthesis of lipids
- Synthesis of proteins
- Breakdown of excess proteins
- Urea
- Glucose
- Fatty acids and glycerol
- Amino acids
32.Which of the following is an example of a metabolic reaction that synthesises a larger molecule from smaller ones?
Medium
- ABuilding a complex carbohydrate from glucose molecules
- BBreaking down glucose during respiration
- CBreaking down excess proteins to form urea
- DBreaking down lactic acid in the liver
33.Place the following statements in the correct order to describe how lactic acid is removed from the body after vigorous exercise.
Medium
- Lactic acid is produced in the muscles by anaerobic respiration
- Blood flowing through the muscles transports the lactic acid to the liver
- Lactic acid is converted back into glucose in the liver
- Oxygen is used to break down the lactic acid into carbon dioxide and water
34.Which statement correctly describes the behaviour of enzymes in muscle cells as lactic acid builds up during vigorous exercise?
Medium
- ALactic acid lowers the pH, which can denature the enzymes
- BLactic acid raises the pH, which can denature the enzymes
- CLactic acid has no effect on the enzymes in muscle cells
- DLactic acid provides extra oxygen for the enzymes to work faster
35.Which of the following statements correctly compare aerobic and anaerobic respiration? (select all that apply)
Medium
- AAerobic respiration requires oxygen but anaerobic respiration does not
- BAerobic respiration releases more energy per glucose molecule than anaerobic respiration
- CAnaerobic respiration completely breaks down glucose
- DAerobic respiration produces carbon dioxide and water
- EAnaerobic respiration in animals produces ethanol and carbon dioxide
36.A yeast cell and a human muscle cell both respire anaerobically. Which row correctly shows the products formed in each cell?
Medium
- AYeast: ethanol and carbon dioxide; Muscle: lactic acid
- BYeast: lactic acid; Muscle: ethanol and carbon dioxide
- CYeast: ethanol and carbon dioxide; Muscle: ethanol and carbon dioxide
- DYeast: lactic acid; Muscle: lactic acid
37.Which of the following correctly describes the role of the liver in removing lactic acid after exercise?
Hard
- ALactic acid is transported to the liver and converted back into glucose
- BLactic acid is transported to the liver and converted into ethanol
- CLactic acid is transported to the liver and stored as starch
- DLactic acid is transported to the liver and excreted unchanged in urine
38.A respirometer is used to investigate the rate of respiration in small invertebrates. Which of the following would make the results less reliable?
Medium
- AThe temperature of the water bath fluctuates during the experiment
- BThe experiment is repeated three times at each temperature
- CThe same mass of invertebrates is used in each tube
- DThe manometer is reset before each reading is taken
39.Which of the following best explains why a respirometer cannot be used to measure the rate of anaerobic respiration?
Medium
- ANo oxygen is consumed during anaerobic respiration
- BNo carbon dioxide is produced during anaerobic respiration
- CAnaerobic respiration does not release any energy
- DAnaerobic respiration only occurs in plants
40.A student sets up a respirometer containing germinating peas and soda-lime pellets. The apparatus is left in a water bath at 25°C. Which of the following best explains why the manometer fluid moves along the capillary tube?
Hard
- AOxygen is taken in by the peas, so the gas volume inside the tube decreases and the fluid moves.
- BCarbon dioxide is produced by the peas, so the gas volume inside the tube increases and the fluid moves.
- CThe soda-lime pellets release oxygen, so the gas volume inside the tube increases and the fluid moves.
- DThe peas release heat, which expands the gas inside the tube and pushes the fluid.
41.Complete the word equation for aerobic respiration.
Easy
glucose + oxygen → ____ + ____
42.Calculate the mean volume of air breathed per minute when running at 5 metres per second. Give your answer to one decimal place.
Medium
43.Name the product of anaerobic respiration that can cause cramp.
Easy
44.Identify the sub-cellular structure where respiration takes place.
Easy
45.Complete the following sentence about respiration. Use each word once, more than once or not at all.
Medium
Respiration releases energy from ____. There are two types of respiration that occur in animal cells: ____ respiration occurs in the absence of ____ and produces a ____ amount of energy. ____ respiration occurs when ____ is present and produces a ____ amount of energy.
46.Complete the sentence about metabolism.
Easy
Metabolism is the sum of all the ____ in a cell or the body.
47.Name the sub-cellular structure where most aerobic respiration takes place.
Easy
48.A runner's stroke volume is 0.18 dm³ and heart rate is 150 beats per minute. Calculate the cardiac output using: cardiac output = stroke volume × heart rate. Give your answer in dm³ min⁻¹.
Medium
49.Complete the sentence about metabolism. Use each word once.
Medium
Metabolism is the sum of all the ____ in a cell or the body.
50.Complete the word equation for anaerobic respiration in animals.
Medium
glucose → ____
51.A respirometer measures oxygen consumption. The capillary tube has a radius of 0.1 cm and the manometer fluid moves 3 cm in one minute. Using the formula πr²h, calculate the volume of oxygen consumed in cm³ min⁻¹. Use π = 3.14.
Medium
52.A respirometer has a capillary tube of radius 0.1 cm. The manometer fluid moves 5 cm in 2 minutes. Using πr²h (take π = 3.14), calculate the rate of oxygen consumption in cm³ min⁻¹. Give your answer to 3 decimal places.
Medium
53.Devise an investigation to compare the mean number of breaths per minute for men with the mean number of breaths per minute for women when running at 5 metres per second on a running machine.
Medium
54.State the reactants and the products of aerobic respiration in animals, and name two substances that are not involved in aerobic respiration in animals.
Medium
55.Explain why the concentration of lactic acid in the blood increases at running speeds greater than 18 km h⁻¹.
Hard
56.Describe the process that occurs in the human body during an oxygen debt.
Hard
57.Explain why the concentration of lactic acid in the blood increases steeply at running speeds above 18 km h⁻¹.
Hard
58.Calculate the mean volume of air breathed per minute when running at 5 metres per second. Give your answer to one decimal place.
Medium
- A60 dm³
- B80.1 dm³
- C66.7 dm³
- D73.4 dm³
59.A runner's stroke volume is 0.18 dm³ and heart rate is 150 beats per minute. Calculate the cardiac output using: cardiac output = stroke volume × heart rate. Give your answer in dm³ min⁻¹.
Medium
- A30 dm³ min⁻¹
- B27 dm³ min⁻¹
- C33 dm³ min⁻¹
- D24 dm³ min⁻¹
60.A respirometer measures oxygen consumption. The capillary tube has a radius of 0.1 cm and the manometer fluid moves 3 cm in one minute. Using the formula πr²h, calculate the volume of oxygen consumed in cm³ min⁻¹. Use π = 3.14.
Medium
- A-0.9058 cm³ min⁻¹
- B2.0942 cm³ min⁻¹
- C0.0942 cm³ min⁻¹
- D1.0942 cm³ min⁻¹
61.A respirometer has a capillary tube of radius 0.1 cm. The manometer fluid moves 5 cm in 2 minutes. Using πr²h (take π = 3.14), calculate the rate of oxygen consumption in cm³ min⁻¹. Give your answer to 3 decimal places.
Medium
- A1.0785 cm³ min⁻¹
- B0.0785 cm³ min⁻¹
- C2.0785 cm³ min⁻¹
- D-0.9215 cm³ min⁻¹

Thẻ ghi nhớ

What is cellular respiration?

An exothermic chemical reaction that continuously occurs in living cells, releasing energy from glucose.

Why is respiration described as an exothermic reaction?

Because it transfers (releases) energy to the surroundings.

State three ways organisms use the energy released by respiration.

For chemical reactions to build larger molecules, for muscle contraction (movement), and for keeping warm.

Write the word equation for aerobic respiration.

glucose + oxygen → carbon dioxide + water

Write the balanced symbol equation for aerobic respiration.

C6H12O6 + 6O2 → 6CO2 + 6H2O

Where does most of aerobic respiration take place in a cell?

In the mitochondria.

Write the word equation for anaerobic respiration in animals (muscles).

glucose → lactic acid

Write the balanced chemical equation for anaerobic respiration in animals.

C6H12O6 → 2C3H6O3 (one molecule of glucose breaks down into two molecules of lactic acid)

Write the word equation for anaerobic respiration in plants and yeast.

glucose → ethanol + carbon dioxide

Write the balanced chemical equation for anaerobic respiration in yeast.

C6H12O6 → 2C2H5OH + 2CO2

What is fermentation?

Anaerobic respiration in yeast cells, which produces ethanol and carbon dioxide.

State two industrial processes that rely on fermentation by yeast.

Making bread (carbon dioxide makes dough rise) and making alcoholic drinks (ethanol is the alcohol).

Why does anaerobic respiration release much less energy than aerobic respiration?

Because the breakdown (oxidation) of glucose is incomplete, so energy remains stored in the products such as lactic acid.

How do the products of anaerobic respiration differ between animals and yeast?

Animals produce lactic acid only; yeast (and plants) produce ethanol and carbon dioxide.

Which type of respiration requires oxygen?

Aerobic respiration; anaerobic respiration takes place without oxygen.

How does the body respond to the increased energy demand during exercise?

Heart rate, breathing rate and breath volume all increase, supplying more oxygenated blood to the muscles and removing more carbon dioxide.

When does anaerobic respiration occur in muscles during exercise?

When vigorous exercise means the body cannot supply enough oxygen to the muscles for aerobic respiration.

What is oxygen debt?

The amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.

Why does breathing rate and heart rate stay elevated after vigorous exercise?

To supply the extra oxygen needed to break down (repay) the lactic acid, and to remove the extra carbon dioxide produced.

Give two ways the body deals with the lactic acid produced during exercise.

It can be oxidised with oxygen to form carbon dioxide and water, or transported in the blood to the liver and converted back into glucose.

Why do muscles become fatigued during long periods of vigorous activity?

Lactic acid builds up, lowering the pH and making conditions acidic, which denatures enzymes so muscles stop contracting efficiently.

Define metabolism.

The sum of all the reactions in a cell or the body.

Name the storage carbohydrates made from glucose in plants and in animals.

Starch (energy storage in plants) and glycogen (energy storage in animals).

What is cellulose used for in plants?

It strengthens plant cell walls.

How are lipids synthesised?

One molecule of glycerol combines with three fatty acids.

How are amino acids and proteins made?

Glucose and nitrate ions are used to form amino acids, which are then used to synthesise proteins.

What happens to excess proteins in the body?

They are broken down to produce urea, which is excreted.

What do respirometers measure?

The rate of oxygen consumption during aerobic respiration in organisms such as seeds or invertebrates.

Why are soda-lime pellets used in a respirometer?

To absorb the carbon dioxide produced, so the change in gas volume measured is due to oxygen consumption.

Why can a respirometer not be used to measure anaerobic respiration?

Because no oxygen is consumed during anaerobic respiration.

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